Abstract: Ultrasonic was applied to assist the catalytic aquathermolysis reaction of heavy oil, and the effect of catalyst and ultrasonic on the physical and chemical properties of Shengli Gudong heavy oil was investigated. Compared to catalytic aquathermolysis reaction, the results of ultrasonic assisted catalytic aquathermolysis indicate that the viscosity of heavy oil is reduced by 86.2%, and the composite technology can further decrease the average molecular weight of heavy oil, increase the saturate and aromatic contents, decrease the resin and asphaltene contents, improve the mol ratio of n_H/n_C, and decrease the heteroatoms content of heavy oil. The results of dynamic simulation experiments show that in-situ ultrasonic assisted catalytic aquathermolysis exhibits good performance with the 53.91% heavy oil recovery and 80.5% viscosity reduction. The experimental results prove that the combination of ultrasonic and catalyst has a synergetic effect, which attributes to the reduction of viscosity and improvement of heavy oil quality.